The present invention relates to synchronization of signals, and more particularly to synchronization of digital audio with digital video for video field accurate recording on a digital disk video recorder.
There exists an audio/video synchronization problem that is caused by the actual one part per thousand, i.e., 60.0 Hz * 1000/1001=59.94 Hz, fractional sample rate offset of 525/60 video relative to its nominal 60 Hz field rate. Thus there are a fractional number of 32 kHz, 44.1 kHz or 48 kHz audio samples, i.e., 533.867, 735.735 and 800.8 respectively, in the time span of one video field. The smallest number of video fields which contain an integer number of audio samples for these rates, or the minimum field denominator (mfd), is shown in the Table of FIG. 1, i.e., 15 fields for 32 kHz yielding 8008 samples, 200 fields for 44.1 kHz yielding 147147 samples, and 5 fields for 48 kHz yielding 4004 samples. These minimum number of samples represent a minimum sample quotient (msq) for each respective field denominator.
Prior methods for solving this problem have relied upon one of two methods:
1. Reducing the audio sample rate by one part per thousand, rounding up the published rate, i.e., by publishing enough significant digits to show the error, and calling that rate "synchronized to video." Thus 44.056 . . . kHz becomes "44.1 kHz synchronized to video" and 47.952 . . . kHz becomes "48 kHz synchronized to video." This approach is misleading to the consumer and incompatible with ANSI standard sample rates.
2. Blocking the audio data into unequal blocks of audio. Digital video tape recorders format data into a five frame, i.e., ten field, sequence using multiple, unequal audio blocks of 160 and 161 samples. This unequal block format also requires a separate linear control track containing the frame sequence, and is suboptimal for field-based digital disk recording.
What is desired is a process for synchronization of digital audio with digital video that does not restrict the sample rate or rely upon unequal block formatting so that any sample rate that yields a rational and sufficiently small "mfd" and resultant "msq" may be accommodated.